1. Field of the Invention
This invention relates to an improvement in a focus detecting device having focus detecting means for detecting a state of focus and focusing state indicating means for indicating a result of the detection made by the focus detecting means.
2. Description of the Related Art
Control modes heretofore employed for automatic focus adjustment by cameras include a mode called the one-shot AF (automatic focusing) mode in which a focus detecting process and a driving process of focus adjusting means are repeated until an in-focus state is obtained. And the driving process of the focus adjusting means is brought to a stop once the in-focus state is obtained. Another control mode is the servo AF mode in which, with the focus detecting process and the driving process of the focus adjusting means repeated until an in-focus state is obtained like in the one shot AF mode, these processes are further performed even after the detection of the in-focus state.
In respect of means for informing the operator of the camera, or a person or persons who are objects of shooting, of an in-focus state upon detection of the in-focus state as a result of focus detection, there have been employed a method of indicating attainment of the in-focus state by a sound generator mounted on the camera or a method of indicating it by a light emitting element such as an LED disposed within a viewfinder. An arrangement made to permit a shutter release only when an in-focus state is attained and to inhibit any shutter release in the event of an out-of-focus state may be also considered to be a sort of method of indicating an in-focus state.
In the servo AF mode mentioned above, an out-of-focus state, or a defocused state, is obtained in a case where a distance between the camera and the object suddenly changes or where the object comes outside of a focus detecting range. In such a case, the camera operator or the persons who are the objects of shooting must be informed of the out-of-focus state by the above-stated methods of indication. Further, when an in-focus state is attained again by a panning operation on the camera or by driving the focus adjusting means, it is necessary to indicate again that the in-focus state is reattained.
However, in the event of a fast moving object or when using a telephoto lens that causes excessive camera shaking due to hand vibrations, in-focus and out-of-focus states frequently alternate with each other to cause the state of indication by focus indicating means to become a nuisance. Such a state of indication is offensive to the eye in a case where it is effected by a light, or to the ear where it is effected by a sound, and thus hinders concentration of attention on a shooting operation. Especially in the case of indicating means for indicating by a sound, it tends to give a disagreeable feeling to many people as the sound propagates over the whole neighborhood of the camera.
To avoid this trouble, a method of generating no in-focus state indicating sound in the servo AF mode has been contrived, as disclosed in U.S. Pat. No. 4,777,504. The method, however, completely eliminates the in-focus state indicating sound and, therefore, has presented a problem in that the camera operator cannot readily make a discrimination between in-focus and out-of-focus states.